Documentation improvements (#2069)

* docs: fix documentation in various places

All stores: resolveID returns a nullable Snowflake
GuildAuditLogs: ActionType also can be ALL
MessageEmbed: make files property show up in the docs
ClientApplication: resetSecret and resetToken return a promise
ClientManager: status is readonly
Guild: features is an array of strings and ban no longer accepts a number or string
Guild: ban method no longer accepts a string or number
GuildMember: ^
RichPresenceAssets: small and large Image are Snowflakes, also fixed parameter documentation for small and large image url method
WebhookMessageOptions: file property is no longer a thing

* docs: improve GuildAuditLogs documentation

Prefix types with AuditLog to avoid confusion
Document GuildAuditLogs' static Targets and Actions properties and add necessary typedefs
Use typdefs over primitives where possible.

* fix documentation for Guild#defaultRole

src/structures/MessageEmbed.js

@@ -132,12 +132,12 @@ class MessageEmbed {
       proxyIconURL: data.footer.proxyIconURL || data.footer.proxy_icon_url,
     } : null;
 
-    /**
-     * The files of this embed
-     * @type {?Object}
-     * @property {Array<FileOptions|string|MessageAttachment>} files Files to attach
-     */
     if (data.files) {
+      /**
+       * The files of this embed
+       * @type {?Object}
+       * @property {Array<FileOptions|string|MessageAttachment>} files Files to attach
+       */
       this.files = data.files.map(file => {
         if (file instanceof MessageAttachment) {
           return typeof file.file === 'string' ? file.file : Util.cloneObject(file.file);
@@ -158,7 +158,7 @@ class MessageEmbed {
 
   /**
    * The hexadecimal version of the embed color, with a leading hash
-   * @type {string}
+   * @type {?string}
    * @readonly
    */
   get hexColor() {